1. Field of the Invention
The present invention relates to a memory apparatus and memory control method.
2. Description of the Related Art
In recent years, scanners, video cameras, and the like have prevailed as input devices. Also, various color printers using an ink-jet system, dye sublimation system, electrophotographic system, and the like have prevailed as output devices. These color input and output devices respectively have unique color spaces (device color spaces). In order to print (display) data read by an input device by an output device, processing for converting the color space of the input device into that of the output device (to be referred to as “color space conversion” hereinafter) is required. For example, when RGB image data scanned by a scanner is to be printed, the RGB color space of the scanner is converted into a standard color space (e.g., AdobeRGB proposed by Adobe Systems Incorporated). After that, the standard color space is converted into a CMYK color space defined by cyan, magenta, yellow, and black as that of color materials (inks or toners) of a printer.
Even in identical RGB color spaces such as RGB color spaces of a scanner and monitor, color conversion is done if they have different color space characteristics (color gamuts). More specifically, when an image scanned by a scanner is to be displayed on a monitor, conversion from a scanner RGB color space to a monitor RGB color space is required to attain color matching.
As one of such color conversion processing methods, a color conversion method that combines a three-dimensional lookup table (3D-LUT) and interpolation operations is known. As an interpolation operation method, tetrahedral interpolation disclosed in GB1595122, EP0969413, or the like is known.
However, with the color conversion method based on 3D-LUT+interpolation, when the number of grids per axis of the 3D-LUT is increased to improve the color conversion precision, the size of the LUT increases by the third power for three dimensions. Also, a digital camera to which a color filter other than RGB is added to improve the color reproducibility is available. In this case, the size of the LUT increases by the number of grids to the fourth power, thus requiring a huge memory size.
On the other hand, some output apparatuses such as printers or the like use many color materials (inks) to improve the color reproducibility, gray balance, and granularity. In this case, the LUT size increases in proportion to the number of color materials.
In order to reduce the cost of the LUT, a color conversion method which stores all data of the LUT in a storage (memory) which has low cost but low speed, and loads only data required in arithmetic operations onto a high-speed cache has been examined.
However, in such cache mechanism, some natures of input data result in poor efficiency. For example, a printer handles objects having different natures such as text, line image, photo, graphics, and the like. However, the number of colors used in text and line image objects is considerably small, and continuity of colors is small. However, if the number of entries of a tag is insufficient, the hit rate is low, resulting in poor efficiency. On the other hand, photo and CG objects, and the like include many moderate gradation parts, and coherence between pixels is high. However, if the number of entries of a tag is large, the fill efficiency of a cache deteriorates, resulting in poor data conversion efficiency.